This invention relates to novel compositions of matter useful as lithographic photosensitizers. More specifically, the present invention relates to novel storage stable diazo photosensitizers useful in the manufacture of lithographic printing plates. Still more particularly the instant invention relates to novel lithographic photosensitizers which are optionally blended with a suitable dye and a compatible resin in an acceptable solvent system to form compositions which when applied to substrates form commercially satisfactory lithographic printing plates having extended shelf lives.
It has been a problem in the past to produce commercially satisfactory lithographic printing plates which retain their ability to be effectively exposed and developed many years after their original manufacture. Planographic printing plates must be carefully prepared so as to maintain their ability to differentiate between hydrophilic and oleophilic areas on its surface.
The prior art has described a plethora of photosensitive compositions which may be employed to produce such plates. One such example is the condensation product of paradiazo diphenyl amine with paraformaldehyde which has subsequently been reacted with a sulfonic acid. Typically, the shelf life of materials which have been used in the past to form such plates is less than two years and usually from about 1 year to 11/2 years.
The present invention provides a lithographic printing plate employing certain specific photosensitizers wherein the obtained shelf life is in excess of five years.